In vitro characterization of GSK2556286 in combination with bedaquiline and pretomanid against Mycobacterium tuberculosis

: GSK2556286 (GSK286) is a novel drug candidate with a cholesterol-dependent mode of action that has shown promising in vivo potential to improve tuberculosis treatment when combined with bedaquiline (B) and pretomanid (Pa). This study explored the in vitro activity of GSK286 alone and in combination with B and Pa, using extracellular and intracellular dose-response time-kill assays against different Mycobacterium tuberculosis (Mtb) strains. GSK286 demonstrated media-specific activity, inhibiting Mtb growth only in cholesterol- and propionate-containing media, with slight activity against both extracellular and intracellular Mtb. The Mtb strain overexpressing Mtb adenylyl cyclase Rv1625c exhibited higher susceptibility to GSK286, whereas the Rv1625c mutant was more resistant. This confirms GSK286's mechanism of action linked to Rv1625c. GSK286 combined with BPa was bactericidal, although the main driver of this interaction was observed between GSK286 and B, with potency comparable to that of the triple BPa + GSK286 regimen, both extracellularly and intracellularly. These findings suggest that GSK286 may be a promising companion to B, with or without Pa, particularly under conditions with a sub-optimal B dose, where the GSK286 + B interaction was more clearly observed. These studies offer new insights into this drug combination to guide future research toward better tuberculosis treatments.